For the drying of lumpy solid materials wetted with solvents, horizontally or near-horizontally arranged externally heated cylindrical apparatus with double walls is used (J. H. Perry: Chemical Engineers' Handbook, page 1712). The solvent is removed from the solid material by a vacuum suction during the drying process and is discharged from the upper part of the equipment. The rotary drum-type vacuum drying apparatus is of intermittent operation, and its filling and draining are cumbersome. Its applicability is limited, since it can be used only for the drying of round, non-sticky, lumpy materials. The material may adhere to the inner surface of the cylinder, an anti-heat conductive layer may occur, and thus the heat utilization is relatively unfavorable. Rotation of the drum with the lumpy material to be dried requires relatively high power consumption.
For the purpose of extracting the solvent remaining in the solid material after the extraction of animal organs and ground plants with solvent, evaporator-type solvent extracting devices are used. Such an apparatus is described for instance in the journal titled: "Paper of Pharm." (USSR, page 27-30/1966/). The solid material containing the solvent is continuously pulped with hot water and the obtained pulp is delivered into the uppermost cylinder of double-walled, heatable, horizontal twin cylinders arranged one above the other.
The solids free of solvents pass out of the bottom cylinder. The extracted solvents pass out of the upper part of each cylinder. The interiors of the cylinders are each provided with a rotary screw conveyor for the purpose of improving the heat transfer, and for the longitudinal delivery of the solids simultaneously with mixing. The heat transfer takes place through the wall and/or with steam conducted into the suspended solid material. A disadvantage of this apparatus--among others--is the high risk of breakdown of the screw conveyor, since the granulated plants may contain brittle, lumpy material (e.g. stones, pieces of metal) which may lead to stopping the screw conveyor or to breakage of the drive by getting jammed between the screw and the wall. Rotation of the screw requires high power consumption. The value of heat transfer and heat utilization is low.
The grading screw type cooling crystallizer described in "Dr. Mucsai L.: Kristalyositas" (Crystallization), Muszaki Konyvkiado, Budapest, 1971, page 151, is known as a crystallizer apparatus. The grader of the grading screw type cooling crystallizer is provided with a sloping trough-shaped bottom, on the lower part of which the larger crystals are deposited. These are removed from the trough by the screw. The mother liquor flowing out of the grader flows back into the mother liquor tank together with the smaller crystals, from where it passes into the cooling system. The disadvantage of this process is that the method of grading of two fractions--i.e. to the material removed with the screw and returned with the mother liquor--is cumbersome, since the grading is regulated by the rate of the flowing medium, while at the same time the crystallization process is a function of the flow rate.
Freezing of the lumpy materials of soft consistency (e.g. meat industry small animal organs, soft fruits, etc.) is often necessary in the food industry. At the present time, freezing tunnels or fluidization freezers are used for the purpose. In the former, the movement of the material from the input to the output takes place with a specially formed belt, and the heat extraction for the freezing takes place with cold air flowing above the material; while in the latter, the cold air passes through the mass of solids, the material being moved during the process of freezing, whereby the rate of cooling is increased.